EARTH HISTORY
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EARTH HISTORY. Chapter 6 review. THREE FUNDAMENTAL PRINCIPLES. 1. UNIFORMITARIANISM :. -The processes that shape the Earth today are the same processes that occurred in the geologic past. “The present is the key to the past”. 2. ORIGINAL HORIZONTALITY.

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EARTH HISTORY

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Earth history

EARTH HISTORY

Chapter 6 review


Earth history

THREE FUNDAMENTAL

PRINCIPLES

1. UNIFORMITARIANISM:

-The processes that shape the Earth today are the same processes that occurred in the geologic past

“The present is the key to the past”


Earth history

2. ORIGINAL HORIZONTALITY

-Sedimentary rock layers are ALWAYS laid down in horizontal layers, until some other process alters them


Earth history

3. SUPERPOSITION

-The bottom layer of horizontal sedimentary rock layers is always the oldest, UNLESS the layers have been overturned or have had older rock formed on top of it

*The lower layers must first be in place before the next layer can be deposited


Earth history

YOUNGEST

OLDEST


Earth history

Igneous Extrusions & Intrusions

Extrusion:

When molten rock flows on the Earth’s surface forming an igneous rock


Earth history

Intrusion:

Occurs when magma squeezes between layers of pre-existing rock beneath the Earth’s surface

-Causes surrounding layers to metamorphose (Contact metamorphism)


Earth history

FOLDS AND FAULTS

Folds and Faults are always

younger than the original

rock layers

Fold:

-bends in rock layers produced by movements of the earth’s crust

Faults:

-breaks in the rock where shifting of rock layers has occurred, often associated with earthquakes


Earth history

Fossils

-Preserved remains or trace evidence of a plant or animal living in the past

Fossils reveal

clues to ancient

environments

Mrs. Sharp


Earth history

Index Fossils: Fossils that are found geographically widespreadand lived for

a short period of time

By comparing index fossils in various

locations on Earth, it is possible to

correlate (match) the relative ages

of the rocks in which they appear

“Geographically

widespread” means the

index fossils are found

in more than one rock column

Lived for a “short

period of time” means

the index fossils are found in only one layer


Earth history

HOW CAN ROCKS

BE CORRELATED?


Earth history

What is Correlation?

When geologists try to match rock outcrops in different locations to see if they formed at the same time.

  • How to correlate (match) rock layers:

  • Similarity of rock types

  • Matching index fossils

  • Volcanic ash layers used as time

  • markers


Earth history

Relative Ageof rocks: (sequence)

The age of a rock layer in

comparison to its surrounding layer

-Uses rock similarity, fossil

evidence, and volcanic time markers

to determine its order of occurrence

Absolute Ageof rocks: (true age)

The age of a rock layer in years

-Uses radiometric dating to determine age--radioactive decay


Earth history

Radiometric Dating of Rocks

Radioactive decay is the process by

which the natural breakdown of

unstable atoms of an element occurs, releasing particles and energy (heat), and changes that element’s atoms into a

new element

Example: it takes 4.5 billion years for uranium 238 to change into lead 206


Earth history

Radioactive decay is NOT AFFECTED by temperature (heat) or pressure!

Radioactive decay

occurs at a constant

rate known as half-life.


Earth history

HALF-LIFE:

Half-life is the rate (time) it takes for one-half of the amount of original material to decay

If we know the half-life of a radioactive material, the age of the material can be determined by measuring the amount of decayed material in the sample.

ESRT pg. 1 Radioactive Decay Data chart


Earth history

Some radioactive substances have a

Short half-life: Carbon 14

-Good for dating recent organic

remains (between 1,000-50,0000 yrs.)

238

206

Uranium

decays to Lead

Long half-life: Uranium238

-Good for dating much older rocks

(a very long half-life) - it takes 4.6 billion years for uranium to decay to lead


Earth history

Example:

The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing

organism shows the original amount of

Carbon-14 was 2.0 grams.

(2.0g _____ _____)

1.How many half-lives did the sample

undergo?

2.Multiply this by the half-life for

Carbon-14 (ESRT)


Earth history

Example:

The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing

organism shows the original amount of

Carbon-14 was 2.0 grams.

(2.0g  1.0g  0.5g)

1.How many half-lives did the sample

undergo?

2.Multiply this by the half-life for

Carbon-14 (ESRT) Answer: 2 x 5,700 = 11,400 yrs.


Earth history

Example:

The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing

organism shows the original amount of

Carbon-14 was 2.0 grams.

(2.0g  1.0g  0.5g)

1.How many half-lives did the sample

undergo? 2

2.Multiply this by the half-life for

Carbon-14 (ESRT)


Earth history

Example:

The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing

organism shows the original amount of

Carbon-14 was 2.0 grams.

(2.0g  1.0g  0.5g)

1.How many half-lives did the sample

undergo? 2

2.Multiply this by the half-life for

Carbon-14 (ESRT)


Earth history

Example:

The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing

organism shows the original amount of

Carbon-14 was 2.0 grams.

(2.0g  1.0g  0.5g)

1.How many half-lives did the sample

undergo? (how many times did it decay)

2 half-lives

2.Multiply this number by the half-life for

Carbon-14 (ESRT) Answer: 2 x 5,700 yrs.= 11,400 yrs.


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